Proteasome inhibitors are currently used as chemotherapeutic drugs because of their ability to block NF-B, a transcription factor constitutively activated in many different types of human cancer. In the present study, we demonstrate that proteasome inhibitors induce cell death in endometrial carcinoma cell lines and primary explants but, instead of blocking NF-B, they increase its transcriptional activity. Proteasome inhibitors induce phosphorylation of IKK␣/␤, phosphorylation and degradation of IB␣, and phosphorylation of the p65 NF-B subunit on serine 536. Proteasome inhibitor-induced NF-B activity can be blocked by a non-degradable form of IB␣ or dominant negative forms of either IKK␣ or IKK␤. Lentiviral delivery of shRNAs to either IKK␣ or IKK␤ cause blockade of NF-B transcriptional activity and inhibit phosphorylation of p65 on serine 536, but has no effect on IBa degradation. These results suggest a role for p65 phosphorylation in proteasome inhibitor-induced NF-B activation. Accordingly, siRNA knockdown of p65 inhibits proteasome inhibitor-induced NF-B transcriptional activity. Our results demonstrate that proteasome inhibitors, including bortezomib, induce cell death on endometrial carcinoma cells and primary explants. However, they activate NF-B instead of blocking its transcriptional potential. Therefore, the concept that proteasome inhibitors are blockers of NF-B activation should be carefully examined in particular cell types.

If intrapleural fibrinolytics are intended to be used, urokinase may be more effective than alteplase in patients with non-purulent CPPE and have a lower rate of adverse events.

We have recently demonstrated that proteasome inhibitors can be effective in inducing apoptotic cell death in endometrial carcinoma cell lines and primary culture explants. Increasing evidence suggests that reactive oxygen species are responsible for proteasome inhibitor-induced cell killing. Antioxidants can thus block apoptosis (cell death) triggered by proteasome inhibition. Here, we have evaluated the effects of different antioxidants (edaravone and tiron) on endometrial carcinoma cells treated with aldehyde proteasome inhibitors (MG-132 or ALLN), the boronic acid-based proteasome inhibitor (bortezomib) and the epoxyketone, epoxomicin. We show that tiron specifically inhibited the cytotoxic effects of bortezomib, whereas edaravone inhibited cell death caused by aldehyde-based proteasome inhibitors. We have, however, found that edaravone completely inhibited accumulation of ubiquitin and proteasome activity decrease caused by MG-132 or ALLN, but not by bortezomib. Conversely, tiron inhibited the ubiquitin accumulation and proteasome activity decrease caused by bortezomib. These results suggest that edaravone and tiron rescue cells of proteasome inhibitors from cell death, by inhibiting blockade of proteasome caused by MG-132 and ALLN or bortezomib, respectively. We also tested other antioxidants, and we found that vitamin C inhibited bortezomib-induced cell death. Similar to tiron, vitamin C inhibited cell death by blocking the ability of bortezomib to inhibit the proteasome. Until now, all the antioxidants that blocked proteasome inhibitor-induced cell death also blocked the proteasome inhibitor mechanism of action.

This study provides information regarding the in vitro effects of proteasome inhibitors on melanoma cell lines, and the molecular mechanisms involved. It also gives support to the future use of such inhibitors in the treatment of patients with melanoma, either administered alone or in combination with other drugs.